Plastic parts are commonly manufactured by a molding process, such as blow molding or injection molding, and then further processed by one or more operations such as boring, drilling, and/or welding.
Welding is a process for joining plastic parts together by melting plastic at a location in each part where a weld joint is to be created, then placing the parts together so that their melt pools merge together, and then allowing the melt pools to solidify and create the finished weld joint.
One type of plastic welding known as contact welding is performed by a heating tool which has a heater element, a hot plate for example, which is heated by a heat source. Thermally conductive parts of the tool which are in contact with the heater element are heated by thermal conduction of heat from the heater element. Other parts not in direct contact with the heater element are exposed to heat radiated by either the heater element and/or parts which have been heated by thermal conduction. A portion of the heater element has a feature which is placed in direct contact with a plastic part to melt plastic at a location where a weld joint is to be created.
Another type of plastic welding known as non-contact welding is performed by a heating tool which has a part which is either a heater, or a heater element heated by a heater, and which is placed a short distance from a surface portion of a plastic part where a weld joint is to be created to radiate heat which melts the plastic at that surface portion.
In both contact welding and non-contact welding, radiated heat lies in the infra-red (IR) band of the electromagnetic spectrum and may comprise wavelengths ranging from short to long. Various types of IR heater elements used in non-contact welding include IR bulbs, wire foil heaters, and ceramic heaters. Even a hot plate heater may be used for non-contact welding if not placed in direct contact with a plastic part.
Because one or more parts of a plastic welding heating tool emit IR radiation, and because that radiation may disperse to some degree before arriving at a surface portion of a plastic part which is to be melted, some IR radiation may be incident on surface portions of a plastic part beyond a portion which is to be melted, and may have an undesired effect on the part.